Process of applying a silver layer on an aluminum electrical contact



Aug. 3, 1965 P. M. H. SEIBERT PROCESS OF APPLYING A SILVER LAYER ON AALUMINUM ELECTRICAL CONTACT Filed Aug. 20, 1962 nqled Par'f'icles oFSilver and flluminum Philip m.

INVENTOR. H. SQ i b e r'l' Qb-h ornaus United States Patent Thisinvention relates to aluminum electrical contacts and more particularlyto a process of applying a silver layer on an aluminum electricalcontact.

A specific use of an aluminum electrical contact embodying the presentprocess is in electric sub-station installations where switches must beoperated automatically or by remote control. Aluminum contacts arenormally subject to oxidization which usually retards the flow ofcurrent and heretofore, it has been normal to employ a silver inlay or asilver plating on one or both of the contacting parts. The silver inlayhas been of around 0.010 inch in thickness and in the event a silverplating is employed the thickness thereof has been not over 0.002 inch.Such inlays or platings wear thin in a relatively short period of timeupon continued operation of an electrical switch or the like on whichthe contacting parts are positioned.

The present invention comprises a process for applying a silver layer onone or both aluminum contacting parts by fusing the silver to thealuminum through heating both the metals and thereby forming anintermediate layer of intermingled silver and aluminum particles of athickness between about .002 inch and .010 inch which is effective toWithstand any of the conditions ordinarily exerted on the contactingparts. By providing a fused layer, the contacting areas are moreabrasive resistant and a relatively large number of contacts can be madewithout failure or undue wear of the fused layer on the contactingparts.

7 It is an object of this invention to provide a process of fusing alayer of silver on an aluminum electrical contact comprising heating thealuminum electrical contact to a temperature of between 400 F. and 900B, thereafter spraying molten silver onto the aluminum contact at asufficient velocity so that the molten silver particles impinge againstthe surface of the heated aluminum contact area and penetrate thealurninum to form an intermediate fused layer of mixed aluminum andsilver particles between .002 inch and .010 inch in thickness. A zinccoating of .0000015 inch is normally provided on the aluminum contactingparts as a protective coating against oxidization and any such zinccoating is vaporized or burned off the surface of the aluminum contactswhen the molten silver is sprayed thereon.

As an example illustrating a specific use of my process, show a switchin the accompanying drawing, forming a of this application, in which:

' 1 is an elevational view of a movable blade pobetween a pair of spacedcontact leaves with the "1g shown in open position and the electricaleas of the blade and the leaves having a fused of intermingled aluminumand silver particles of nckness between .002 and .010 inch;

FIG. 2 is an elevational view of the apparatus shown in FIG. 1 butshowing the blade in closed position and contacting the spaced pair ofleaves whereby electrical contact is made between the leaves through theblade; and,

FIG. 3 is an enlarged sectional view taken through an electrical contactarea of a leaf and showing the several layers there-at.

Referring to the drawing, a switch is shown generally diagrammaticallyand comprises a blade indicated generally by the numeral and spacedcontacting spring leaves indicated generally by the numerals 11 and 12.

3,198,662 Patented Aug. 3, 1965 Blade 10 and leaves 11 and 12 are formedof aluminum with blade 10 positioned between leaves 11 and 12 andadapted for movement between open position shown in FIG. 1 and closedposition shown in FIG. 2. Electrical contact areas 13 are formed on theends of blade 10 and contact areas 14 are formed on leaves 11 and 12.

It is highly desirable to remove any aluminum oxides from the contactingareas to be fused with silver before the present process is applied asthe fusing of silver is retarded by the presence of aluminum oxides.Aluminum oxide has a melting point of around 3600 F. against a meltingpoint of 1220 F. for aluminum and around 1760 F. for silver. To removealuminum oxides from the electrical contacting parts before the presentprocess is applied, it is desirable to employ a zinc immersion treatmentcomprising cleaning the parts with a mild alkaline cleaner, dipping theparts in acid for one to three seconds, rinsing the parts in water, andthen dipping the parts in a zinc oxide bath from one-half to one minuteat 60 to F. with a water rinse thereafter, all as well known in the artunder the term zincating process. Through the immersion treatment, azinc coating of around .0000015 inch in thickness is provided on thealuminum parts and protects the aluminum from surface oxidization for arelatively short period of time.

It is understood that my process may be employed on other types ofaluminum electrical contacts than the specific apparatus shown in thedrawings and that such -apparatus is shown only for the purpose ofillustration. The term part as employed herein is interpreted asincluding all electrical contacting parts such as switches, circuitbreakers, electrical connectors, and the like. In the process of fusingsilver to the aluminum contacts, the aluminum contact areas 13 and 14are heated to a temperature of around 650 F. preferably. Temperaturesbetween 400 F. and 900 F. will work satisfactorily. Before the aluminumcontact areas lose their temperature they are sprayed with molten silverentrained in a stream of gaseous material. For spraying the silver asilver Wire is fed through a metalizing gun which atomizes the wire intoa stream of molten silver particles. The particles are uniformly heatedand the rate of spray is well controlled by the metalizing gun. ismelted by a combination of gases at a uniform rate of speed. The gasescomprise oxygen combined with one of the following: acetylene, propane,butane, or hydrogen. Also, natural or manufactured gas may be combinedwith the oxygen. The gases arebalanced along with compressed air that isalso used to atomize the molten silver and a neutral flame neitheroxidizing nor can bonizing is formed in which the silver wire isatomized. The molten particles of silver are entrained in a stream ofoxygen free air formed from the compressed air and the oxygen mixturewhich stream is at a temperature in excess of 4000 F. The blast of hotair and the finely divided superheated silver particles vaporize thezinc coating on the aluminum contact parts and the molten particles ofthe atomized silver impinge against the aluminum contact parts andpenetrate it to a depth of between .002 inch to .010 inch. Themetalizing gun is held about 4 inches from the surface of the aluminumcontact parts to which the silver is to be fused and the silverparticles move at a maximum velocity of around 225 feet per second.

Referring to FIG. 3 an intermediate layer 16 is formed beneath thesurface of the aluminum contact part and is composed of mixed particlesof silver and aluminum being of a thickness of between .002 inch and.010 inch corresponding to the penetration of the silver particles.

An outer layer 17 of silver is formed of a thickness above .020 inch andis built up on intermediate layer 16 above the surface of the aluminumcontact parts 10, 11 and 12. A thickness of around .030 inch for outerThe silver wire V layer 17 has been found to be preferable althoughthicknesses over .015 inch will work effectively. Thus, particles ofsilver and aluminum are fused in intermediate layer 16 so as to securein permanent fashion outer silver layer 17. The precentage of silver inthe intermediate layer is variable but it increases from its innermostpenetration of the aluminum outwardly to the surface of the connector.After the aluminum contact parts having been sprayed with silver, theyare cooled rapidly in water or a mist which keeps the oxidizing of thesurface of the silver at a minimum during cooling.

From the foregoing it will be understood that I have provided a processfor applying a silver layer on aluminum electrical contact parts byheating the parts and then spraying silver onto the surface at thecontact areas thereof. By removing aluminum oxides and zincating thecontact parts, then heating the contact areas and spraying molten silverparticles at a sufficient velocity, the silver particles penetrate thesurface of the aluminum and form an intermediate layer of intermingledsilver and aluminum particles between .002 inch and .010 inch inthickness thereby fusing the silver and the aluminum. The silver layermay be provided in a minimum of time and any outer zinc coating on thecontact areas is vaporized or burned off by the hot air and other gasesin which the molten silver particles are entrained when the silver issprayed onto the aluminum parts. The term aluminum is employed herein todescribe the contact parts is interpreted as including aluminum alloyedwith other metals.

While I have shown my invention in but one form, it will be obvious tothose skilled in the art that it is not so limited, but is susceptibleof various changes and modifications without departing from the spiritthereof, and I desire, therefore, that only such limitations shall beplaced (a) zincating the surface of the aluminum part to remove anyaluminum oxides from the surface thereof and to form a protective zinccoating thereon,

(b) heating the aluminum contact part to a temperature between 400F.'and 900 F., and

(c) spraying molten silver entrained in a blast of gas under pressureonto the heated aluminum part whereby the gas vaporizes the zinc coatingto remove it from the surface of the aluminum part, said silver beingsprayed at a sufiicient velocity to form a layer of intermingled silverand aluminum particles between .002 inch and .010 inch in thickness onwhich an outer layer of silver may be formed.

2. The process of fusing a silver layer on an aluminum electricalcontact part comprising (a) zincating the surface of the aluminum partto remove any aluminum oxides from the surface thereof and to form aprotective zinc coating thereon,

(b) heating the aluminum part to a temperature between 400" F. and 900F., and

(c) spraying molten silver entrained in a stream of gas under pressureonto the heated aluminum part whereby the gas vaporizes the zinccoating, said silver being sprayed at a velocity on the order of 225feet per second whereby they penetrate the surface of the aluminum toform an intermediate fused layer of mixed silver and aluminum particlesof from .002 inch to .010 inch in thickness and an outer layer of silverof at least .015 inch in thickness on the intermediate layer.

References Cited by the Examiner UNITED STATES PATENTS RICHARD D.NEVIUS, Primary Examiner.

1. THE PROCESS OF FUSING A SILVER LAYER ON AN ALUMINUM ELECTRICALCONTACT PART COMPRISING (A) ZINCATING THE SURFACE OF THE ALUMINUM PARTTO REMOVE ANY ALUMINUM OXIDES FROM THE SURFACE THEREOF AND TO FORM APROTECTIVE ZINC COATING THEREON, (B) HEATING THE ALUMINUM CONTACT PARTTO A TEMPERATURE BETWEEN 400*F. AND 900*F., AND (C) SPRAYING MOLTENSILVER ENTRAINED IN A BLAST OF GAS UNDER PRESSURE ONTO THE HEATEDALUMINUM PART WHEREBY THE GAS VAPORIZES THE ZINC COATING TO REMOVE ITFROM THE SURFACE OF THE ALUMINUM PART, SAID SILVER BEING SPRAYED AT ASUFFICIENT VELOCITY TO FORM A LAYER OF INTERMINGLED SILVER AND ALUMINUMPARTICLES BETWEEN .002 INCH AND .010 INCH IN THICKNESS ON WHICH AN OUTERLAYER OF SILVER MAY BE FORMED.